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[PW_SID:1148295] riscv: lib: Fix address overflow due to large count values in strnlen ZBB path #2492

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[PW_SID:1148295] riscv: lib: Fix address overflow due to large count values in strnlen ZBB path #2492

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22 changes: 16 additions & 6 deletions arch/riscv/lib/strnlen.S
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Original file line number Diff line number Diff line change
Expand Up @@ -17,6 +17,7 @@ SYM_FUNC_START(strnlen)
__ALTERNATIVE_CFG("nop", "j strnlen_zbb", 0, RISCV_ISA_EXT_ZBB,
IS_ENABLED(CONFIG_RISCV_ISA_ZBB) && IS_ENABLED(CONFIG_TOOLCHAIN_HAS_ZBB))

strnlen_generic:

/*
* Returns
Expand All @@ -27,15 +28,17 @@ SYM_FUNC_START(strnlen)
* a1 - Max length of string
*
* Clobbers
* t0, t1, t2
* t0, t1
*/
addi t1, a0, -1
add t2, a0, a1
mv t1, a0

1:
addi t1, t1, 1
beq t1, t2, 2f
beqz a1, 2f
addi a1, a1, -1
lbu t0, 0(t1)
bnez t0, 1b
beqz t0, 2f
addi t1, t1, 1
j 1b
2:
sub a0, t1, a0
ret
Expand Down Expand Up @@ -73,6 +76,13 @@ strnlen_zbb:
/* If maxlen is 0, return 0. */
beqz a1, 3f

/*
* Fallback to generic implementation when count is large enough to
* cause address overflow in the ZBB optimized path
*/
add t4, a0, a1
bltu t4, a0, strnlen_generic /* a0 + a1 overflow */

/* Number of irrelevant bytes in the first word. */
andi t2, a0, SZREG-1

Expand Down
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